THE VACUUM -UV PHOTOABSORPTION SPECTROSCOPY OF THE THREE-MEMBERED RING SYSTEMS C3H6, C2H4O and C2H4S
AND THEIR OPEN CHAIN ISOMERS. R. Locht1, B. Leyh1, H.W. Jochims2 and H. Baumgärtel2.
1Laboratoire de Dynamique Moleculaire, Départment de Chimie, Université de Liège,
Institut de Chimie, Bât. B6c, Sart-Tilman par B-4000 Liège 1, Belgium.
2Institute für Physikalische Chemie, Freie Universität Berlin,
Takustrasse 3, D-14195 Berlin, Germany.
During several years we investigated the vacuum UV photoabsorption, the He(I)- and threshold photoelectron spectra and the photoionization mass spectrometry of many halogenated derivatives of methane [1] and ethylene [2-4]. A very large amount of data has been obtained and their publication are in progress. These data were completed by laboratory work performed in Liège on the translational energy distribution measurements of most of the fragment ions appearing in the mass spectra recorded with He(I), Ne(I) and Ar(II) resonance lines. 6 7 8 9 10 11 12 0.0 0.2 0.4 0.6 Thiirane-C2H4S
Photon Energy (eV)
6 7 8 9 10 11 12 0.0 0.1 0.2 0.3 Oxirane-C2H4O Absor bance log 10 [I0 /I ] 6 7 8 9 10 11 12 0.0 0.2 0.4
V-UV Photoabsorption Spectrum of
Cyclo-C3H6
Another class of
interesting small molecular systems are the
three-mem-bered rings: C3H6 or
cyclo-propane, C2H4O or oxirane,
C2H4S or thiirane and C2H5N
or aziridine. Spectroscopic data related to these systems are very scarce in the literature. No high level quantum mechanical calcula-tions are available. When stable, the open structured isomers are also worth being reinvestigated at higher resolution.
These are a few reasons of a thorough invest-tigation of the photoabsorp-tion and mass spectrometric photoionization of these compounds. The data obtained at BESSY II were completed by laboratory experiments of He(I)-, Ne(I)- and Ar(II)-resonance line photoelectron and photoion kinetic energy spectroscopy of the fragments.
A 3m-NIM
monochro-mator (on the 3m-NIM-2 Fig. 1: Vacuum UV absorption spectra of
beamline) was used, equipped with a 600 ℓ/mm Al-grating. A major disadvantage of this material, however, is its reflectivity gap between 16-18 eV. Entrance and exits slits were adjusted at 10-30 µm allowing a resolution of about 5 000. The photon energy was scanned between 5-25 eV.
Fig.1 shows typical exemples of photoabsorption spectra recorded between 5.5-12.5 eV for cyclopropane, oxirane and thiirane respectively. The high toxicity of aziridine prevent to introduce it in the experimental hall.
Excepting that of cyclopropane, the spectrum of the two other compounds show very sharp and strong features corresponding to Rydberg transitions accompanied by well resolved vibrational fine structure. A close examination of the broad absorption band peaking at about 10.12 eV in cyclopropane reveals also a vibrational progression. The detailed examination and interpretation of the experimental results and the assignment of all these features are in progress.
The photoabsorption spectra have been measured under the same conditions for the
stable open chain isomers of C3H6 and C2H4O, i.e. propene and acetaldehyde.
Ackowledgments.
We gratefully acknowledge the European Community for a financial support through the Contract N° R II 33-CT-2004-506008. R.L. and B.L. wish to thank the Communauté Française de Belgique for an “Actions de Recherche Concertée” (A.R.C.) contract.
References.
[1]. R. Locht, B. Leyh, A. Hoxha, D. Dehareng, H.W. Jochims, H. Baumgärtel, Chem.Phys. 257 (2000) 283; ibid. 272 (2001) 259; 272 (2001) 277.
[2]. R. Locht, B. Leyh, K. Hottmann, H. Baumgärtel, Chem.Phys. 220 (1997) 217. [3]. R. Locht, A. Hoxha, B.Leyh, K. Hottmann, H.W. Jochims, H. Baumgärtel, BESSY Jahresbericht (1996) 160.
[3]. A. Hoxha, R. Locht, B. Leyh, D. Dehareng, K. Hottmann, H. Baumgärtel, Chem.Phys. 256 (2000) 239.
[4]. R. Locht, B. Leyh, H.W. Jochims, H. Baumgärtel, BESSY Jahresbericht (1996) 156 ; ibid. (1999) 251; ibid. (2003) 49.
